function distance = cellDistance
[x, y] = getline;
distance = sqrt((x(1)-x(2))^2+(y(1)-y(2))^2);
% the long edge of the image is 193um in rig 4.
% the long edge of 4x image is 2150um in rig 4.
 distance = distance * 2150/800;
% distance = distance * 193 / 800;